Caption: John Louis Emil Dreyer (1852-1926), Danish-Irish astronomer. Born and educated in Denmark, Dreyer spent his working career in Ireland. He began as an assistant to the 4th Earl of Rosse before moving to Dunsink Observatory, Dublin in 1878. In 1882 he became the director of Armagh Observatory, where he remained until 1916. He compiled the New General Catalogue of Nebulae and Clusters of Stars which is still in use today. He was also a keen historian of science, and wrote a biography of 16th-century astronomer Tycho Brahe. Dreyer was president of the Royal Astronomical Society from 1923-5, having won the society's Gold Medal in 1916.